Heat-transfer characteristics have been determined for the circular finned and unfinned-tube units during the freezing of magnesium chloride hexahydrate (MgCl2.6H2O) used as a phase-change material (PCM) with a melting temperature of 116.7-degrees-C. The effects on the heat-transfer characteristics have been determined of the inlet temperature and the flow rate of air used as the heat-transfer fluid (HTF). With the unfinned-tube unit, the heat-transfer coefficients obtained between the PCM and the tube are larger than the calculated values based on the theory of steady-state heat conduction due to the dendritical crystal growth of PCM. The ratio of the heat-transfer coefficient of the finned- to the unfinned-tube systems is about 3.5 within the finned section and decreases gradually far from the finned section with an increase in crystal volume. The total amounts of heat recovered have been correlated in terms of the Fourier, Stefan, and Reynolds numbers to provide basic design data for circular finned- and unfinned-tube heat-storage units.